Abstract: During the thermal Polymerization of styrene small quantities of dimeric and trimeric styrene are usually formed. In this paper the kinetic character of dimeric and trimeric at temperatures of 137℃ and 180℃ are studied by means of simulation method of an approximate curve of 'S' type. The corresponding kinetic equation is obtained, which is simple in form and clear in physical significance. Compared with Kirchner's theoretical model, this model is in better agreement with experimental results.